Jet engine igniter plug



p 9, 1952 w. A. BYCHINSKY JET ENGINE IGNITER PLUG Filed Feb. 28, 1950 a i if 05 w. e m m a Patented Sept. 9, 1952 JET ENGINE IGNITER PLUG Wilfred A. Bychinsky, Ann Arbor, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application February 28, 1950, Serial No. 146,757

Claims. 1

The present invention relates to ignition devices for fuel burners and more particularly to igniter plugs generally similar to spark plugs employed in the ignition of fuel supplied to the combustion chambers of combustion gas turbines. Such a device is illustrated and described in the application of Donald J. Steeg, Serial No. 47,858, filed September 4, 1948, assigned to the assignee of the present application (now Patent No. 2,526,169 issued October 17, 1950) Because of the exposure of parts of such ignition devices to the high operating temperatures of combustion chambers, substantially large temperature gradients occur introducing thermal stresses in the parts exposed. In ignition devices comprising a shell and insulator with a centrally disposed electrode, exposure of the insulator to the flame in the combustion chamber causes thermal stresses of sufficient magnitude to fracture the insulator structure requiring replacement of the ignition device. Moreover, where the insulator is exposed to the flame, carbon deposits reduce the efficiency of the device requiring frequent inspection and cleaning. Such conditions are unsatisfactory particularly where such devices are used in combustion gas turbines for propelling aircraft.

Accordingly, it is an object of the present invention to provide an igniter plug especially suitable for combustion gas turbines and so constructed and arranged that the insulator is protected from direct contact with the flame in the combustion chamber and that movement of air to the combustion chamber may be utilized to keep the parts cool and clean.

This and other objects are attained in accordance with the present invention by providing an igniter plug in which the insulator is substantially completely shielded from the flame and having means adapted to direct the flow of air to the combustion chamber along the walls of the insulator and the shell.

For a better understanding of the invention reference may be had to the drawing in which Figure l is an elevational view of an igniter plug embodying the present invention; Figure 2 is a fragmentary sectional view of the igniter plug illustrated in Figure 1; Figure 3 is a view taken along the line 33 of Figure 2 and Figure 4 is a view similar to Figure 2 illustrating a modification of the invention.

Referring now to the drawing and particularly to Figures 1, 2 and 3, there is illustrated an igniter plug embodying the present invention and comprising a shell 2 and an insulator 4 centrally dis 2 posed in the shell. The shell is a substantially cylindrical member provided with a mounting bracket 6 illustrated in Figure 3 as having apair of mounting holes 8 which are aligned on an axis offset from the central axis of the igniter plug. By providing mounting holes 8 offset from the central axis of the igniter plug the plug is adapted for one position of mounting in a combustion chamber with the lower portion of the shell exposed to the incoming air as disclosed in the above-mentioned application. To introduce air to the interior of the shell 2 an aperture I0 is provided. The axis of aperture 10 is radial to the central axis of the igniter plug and is disposed in the shell in such a manner that it faces the upstream direction of the combustion air when the igniter is mounted in the combustion chamber and with its axis at an acute angle to the direction of the air stream. Such a disposition of the aperture and igniter in a combustion chamber provides a desirable swirling action of the air around the insulator for even cooling and cleaning. The lower end of the shell 2- is reduced along a substantially conical contour, as shown, and provided with axial slots 12 equally spaced around the shell to form a plurality of inturned electrodes 13. The upper end of the shell is internally threaded, as shown, to receive a connector [4 adapted to clamp the insulator and shell in assembled relationship. The insulator 4 comprises a tapered end portion (6 which extends downwardly from an expanded portion l8 having spaced shoulders 20 and 22. The insulator is formed with an internal bore 24 of varying cross section to provide the shoulders 2'6 and 28 and a recess 38 of sufficient cross-sectional area to receive the terminal end of an ignition cable, not shown.

Disposed in a central bore 24 of the insulator is an elongated electrode 32 which extends downwardly through a recess 34 formed in the lower end and into spaced relation with the ends of the inturned electrodes I3. The electrode 32 is provided at its upper end with an expanded head 33 adapted to engage the shoulder 26. To provide for spacing the electrode 32 in the bore 2 3 it is formed with an enlarged portion 38 having a knurled surface for engaging the wall of the insulator bore. Positioned in the recess 30 is a terminal electrode 40 having an enlarged head 42 adapted to engage shoulder 28. The terminal electrode 40 and electrode 32 are sealed in the insulator bore with an intervening conductive element 44 which provides a seal between the electrodes 32 and 40 and the insulator substantially as disclosed in the Patent 2,248,415 to Schwartzwalder et al., dated July 8, 1941.

In assembling the ignition device the insulator 4 is disposed in the shell 2 with a asket 46 of metal of suitable ductility interposed between the insulator shoulder 22 and a shoulder 48 formed in the wall of the shell 2. A second gasket 50 is placed on the insulator to rest on shoulder 20 and the connector i4 is turned into the shell causing the gaskets to deform and providing a seal between the insulator and shell.

With the ignition device assembled in this manner there is formed an air duct EZ in communication with the aperture [0 and having an increasing cross-sectional area downwardly nan the aperture toward the reduced end of the shell. With the insulator disposed, with its lower end spaced from the inner walls of the electrodes, l,3, as shown, a restricted orifice 54 is formed providing communication between the air duct 52 and the outlet aperture 56 at the lower end of the shell. The reduced orifice 52 eausesa flow of air across the wall of the insulator at the lower end or the insulator and because of the recess 34 the end of the insulator is maintained at a temperature with substantially little temperature gradient. Consequently substantially no internal stresses are set up in the end of the insulator which would induce fractures in the material.

Moreover, the flow of air across the inner walls of the electrodes i3 cools the electrodes to such a degree that the shell and electrodes may be formed of less expensive materials such as steel Whereas heretofore it has been considered necessary to form the electrodes of heat resistant alloy materials. Further, with the "end of the insulator shielded by the electrode structure, it is not in direct contact with the name thus substantiall eliminating heat shock from the flame and deposits of solids which interfere with the eflicient operation of the ign'iter. In connection with the electrode structure it will be understood that an igniter of equally satisfactory performance characteristics may be providedin which the reduced end or the shell is solid or in which spaced aperture's are formed in the walls of the reduced end.

In Figure 4 I have illustrated a modification of my invention which is substantially the same as the igniter illustrated in Figures 1, '2 and 3 except that the shell is formed in two parts. As shown the shell comprises a lower shell 58 and an upper concentric shell 60 of less diameter. The lower shell is formed of a cylindrical member of uniform thickness which has an inwardly pressed annular portion 62 providing a shoulder 64 for seating the insulator. The upper shell 86 has its lower end formed to engage the upper sealing gasket of the igniter and is provided with an annular flange 65 over which the upper end of shell 58 is turned to secure the upper shell 60, the insulator and the lower shell 53 in assembled relationship.

While the embodiments of the present invention as herein disclosed constitute preferred forms, it is to be understood that other forms might be adopted all coming within the scope of the claims which follow.

What I claim as new and desire to secure by Letters Patent of the United States is: v V v 1. In an igniter, a shell having an inlet pas sage and a frusto-conicallend wall providing an electrode structure, said end wall having a passage therein, an insulator having an end portion of reduced cross-sectional area concentrically mounted in said shell with the end thereof shielded by the frusto-conical end wall of said shell, said insulator and shell being spaced to define a duct therebetween of varying cross section in communication with said passage, said duct having a restricted outlet between the end of said insulator and the frusto-conical end wall of said shell, and an electrode centrally disposed in said insulator and projecting beyond the end thereof to cooperate with said shell electrode structure to provide a spark gap.

2. In an igniter, a shell having an air inlet passage and an inwardly tapered castellated end wall providing an electrode structure, an insulator concentrically mounted in said shell and j having an en'd-pbrtion terminating adjacent said H r V plug for combustion gas turbines, a cylindrical member provided with an air inlet passage and an inwardly tapered wall adjacent its endsaid wall having spaced axial slot's therein to provide a plurality of ground electrodes, an insulator; m'ounted within said shell and spaced therefrom to provide a duct in communication with said passage, said insulator having a recessed end adjacent to and encircled by said taperedwall to provide a restricted outletfrom said duct, and an electrode disposed in saidinsulator having one end projecting outwardly fron said recessed end and into spaced relation with the electrodes of said cylindrical h U l lnr an igniter plug for combustion gas turbines a cylindrical member having an inlet opening in its wall and a frusto-conical end portio c omprising a plurality of spaced electrodes providing ja substantially circular outlet of substantiallyless diameter than the interior of said cylindrical member an elongated insulator with a tapered portion and an end with a recess therein, said insulator being mounted in said cylindrieaLrrie rhber with its tapered end poressences "frorh 'said cylindrical member and itsiehd inwardly spaced from said frusto-conical end portionv to provide an annular duct in commiirii'c'ation with said inlet opening and said outlet, "said duct being restricted between the end of said insulator and said frusto-conical end portion and a central electrode embedded in said irisulatonand extending outwardly therefroln into said outlet. passage to form a spark gap with 'saidelectrodes'. p

, 5. In an igniter plug for combustion gas turbines ja Tcylindrical member having an inlet opening in its wall and a frusto-conical end portion comprising a plur'ality of electrodes at onejend providing asubstantially circular outle t o f substantially less diameter than the internal diamfeter of said cylindrical member, a mounting flange secured to said cylindrical inemb'er having mounting holes aligned on an a ds. offset from the central axis of said cylindrical member, an, elongated insulator with 'a tapered portion and an end with a recess therein, said insulator being mounted in said cylindrical membjer with its tapered end portion spaced therefrom and its end inwardly spaced from saidfrusto-conical end portion to provide an annular duct in communication with said inlet opening and said outlet, said duct having a restricted cross-sectional area between the end of the insulator and said frusto-conical end portion, and a central electrode sealed in said insulator, said electrode extending outwardly from the tapered end portion of said insulator and into said outlet to form a spark gap between said electrodes.

6. In an igniter, a lower tubular shell member having a frusto-conical end portion providing a ground electrode for said igniter and an inwardly pressed annular portion forming a shoulder, an insulator having an enlarged mid-portion and a tapered end portion extending therefrom, said insulator being concentrically disposed in said shell member with said mid-portion seating on said shoulder and said tapered end portion terminating within said shell adjacent said frustoconical end portion to provide an annular air space with a restricted annular outlet orifice, said annular air space being in communication with said passage, an upper tubular shell member telescopically disposed within said lower tubular shell member with its end seated on said enlarged mid-portion, means on said upper and lower tubular shell members including a second inwardly pressed portion on said lower shell member for securing them as a unitary shell structure, and an electrode centrally and axially disposed in said insulator.

7. In an igniter, a shell having a constantlyopen inlet port and an inwardly tapered castellated end portion, an elongated insulator mounted in spaced concentric relation within said shell,

said insulator and shell defining an annular duct in communication with said port, the end of said insulator being positioned adjacent the inwardly tapered end portion of said shell to provide said duct with a restricted outlet, and an electrode centrally disposed in said insulator and projecting beyond the end thereof to cooperate with the tapered end portion of said shell to provide a spark gap.

8. In an igniter plug for combustion gas turbines, a cylindrical member provided with an air inlet passage and an inwardly tapered Wall adjacent its end, said wall having spaced axial slots therein to provide a plurality of ground electrodes, an insulator mounted within said shell and spaced therefrom to provide a duct in communication with said passage, said insulator having its end adjacent to and encircled by said tapered wall to provide a restricted outlet from said duct, and an electrode disposed in said insulator having one end projecting outwardly from said recessed end and into spaced relation with the electrodes of said cylindrical member.

9. In an igniter, a shell having a passage in its wall and a frusto-conical castellated end portion providing a ground electrode for said igniter, an insulator concentrically disposed in said shell to provide therebetween an annular space in communication with said passage, said insulator having its end portion terminating within said shell intermediate the ends of the frusto-conical castellated end portion and spaced therefrom to provide a restricted annular orifice as an outlet from said annular space, and an electrode centrally and axially disposed in said insulator.

10. In an igniter, a shell having a passage in its wall and an inwardly tapered end portion providing a ground electrode for said igniter and formed to provide air outlets distributed along the length of the tapered portion, an insulator concentrically disposed in said shell to provide therebetween an annular space in communication with said passage, said insulator having an end portion of decreased cross-sectional area terminating within the end portion of said shell and spaced therefrom to provide a restricted annular orifice as an outlet from said annular space, and an electrode centrally and axially disposed in said insulator, said electrode terminating at the end of said shell.

W ILFRED A. BYCHINSKY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,370,655 Lehr Mar. 8, 1921 1,499,594 Riley July 1, 1924 2,153,598 Steward Apr. 11, 1939 2,493,743 Benson Jan. 10, 1950 2,526,169 Steeg Oct. 17, 1950 

